Testosterone is a 'reward' hormone : your production rises whenever you feel 'successful'. This is why 'visualisation' can be so effective; imagining that you can complete a challenging lift, strongly enough that you can see & feel it happening, will boost your testosterone output & enable you to train harder.

If you can't picture that clearly enough, you can compile a mental 'showreel' of moments in the past when you did succeed at something; running through this will simulate the effects of a successful outcome, and cause a surge in your production of Testosterone.