Spend all energy on battles or tasks just before leveling up to get a free full refill.

: Platforms like WeMod host unofficial trainers that claim to offer "mods" such as unlimited health or stamina, though these may carry risks to your account standing. Native PC Gameplay Methods

If you are looking for a trainer because your game is crashing, note that the PC version has experienced significant stability issues:

Since you're on PC, you can run multiple instances of emulators.