How do you push through working hard during an exercise? I would like techniques to push through mental blocks of what I think I am capable of

I use a heart rate monitor . That way i see that althougj the exercise may feel hard .. if my heart rate is below my targer i know that i can push harder.

I like to listen to audiobooms or podcasts that I enjoy while exercising. I find that this distracts me from what I am doing and allows me to exercise harder and longer. I also pick a book or TV show that I really like and decide to only listen to or watch it while I exercise. That way my motivation to watch a favorite show is linked to my motivation to exercise.

When weightlifting, don't get too hung up on numbers, other than finding the range you want to work in. Go until failure every set, not stopping at a certain number. That will tell you whether the weight is too heavy or too light.
Use mid-set breaks: Just when you get close to the failure point, stop, take a breath, then power out a few extra reps. On the final rep, do a rest-pause: After reaching failure, set the weight down, shake it out, take a couple deep breaths, then go for a few more reps to failure.

I always start by saying to myself “I’ll start with 5 minutes. I can do anything for just 5 minutes.” Then, when things get really hard, I just count to 10 until that set or interval is over. It helps take my mind off whatever is happening.

Two situations came to my mind. First is when I'm running and I think I can go further. Then I use a meditation practice to visualize that though from the outside and the let it go and focus on my breath. After a few minutes I find myself thinking on something else. The second situation is when stretching and I think I've reached my limit. Then what I do is to relax completely on that limit and when I feel comfortable the push a bit more. In all situation take care to not go too far beyond your capacities, or you can hurt yourself.

I try to enjoy every activity. I mostly run, so i watch heart rate, what should stay at 70%. This way i can breath normally and i have a great workout.

Concentrate on the breath breathing deeply from the diaphragm. If there is an exercise pose u find difficult breathe and visualise yourself successfully acheiving it.

I usually dance to the oldies to work out some of the stiffness in my joints. Even though I walk with a cane, I find I am walking faster . I never thought I would be able to do the quicker walking. You just have to make up your mind you can do it and you will find you can.

If you don’t like or even hate exercising, just think about after your done exercising and what you’ll do then and reward yourself. I also recommend a fitness app if you really need it.

I really focus in on my goal and block out the aches and the exhaustion, and the lazy thoughts and imagine what it will feel like when I reach that goal.

At the moment I mostly do pilates and running. For pilates it really helps me to do it in a group with an instructor. I can "outsource" some of my willpower to her. She will tell me to keep going when I can't do it anymore. I notice the difference when I try to do it by myself. I stop much earlier.
Running I enjoy a lot so it is much easier to push myself. So maybe it's also about finding the right excercise for you.
Finally, just signing up for some competitions (if available for your sport) or working out together with a friend can help a lot as well.
Hope this helps!