In Pokemon Platinum, I put a Bidoof in the daycare (there was no way I was going to manually evolve it into bibarel) and had taught it HM and TM moves. It turns out the daycare deleted every one, and I need TM strength back! Is there any way I can get it back?
Just reteach it to your Bidoof.
Strength isn't a TM - it's an HM. HMs are reusable, therefore you should easily reteach it Strength. So don't worry. :)
Hope I helped. :)