Rebuilding trust with tooth brushing ☹️

I've been very lucky compared to some, and my toddler has never had an issue with brushing his teeth. He would willingly open his mouth and dance to the tooth brushing song as I did it every day.

However

Lately, I've just been out of it (first an injury, then kidney infection, now pregnant) and so my husband has taken over the night routine. He's not as confident/skilled with some of the tasks like I am, and accidentally made our son gag when brushing his teeth. He thinks the toothbrush just went a little too far back 😔 He's completely distraught about it, especially since now our son freaks out whenever we try to brush his teeth.

He shuts his mouth tight, cries, runs to me, etc. But he won't even let me try. We've switched toothbrushes, let him pick out new toothpaste, watch episodes on toothbrushing, etc. I give him the toothbrush to use, and it works for a bit, but obviously he's not doing a great job (he's 3!) so I need to go in and get the tricky spots. I've even let him brush my teeth with my toothbrush and he just thought it was the funniest thing lol

I really don't want to force him and cause more stress. He's completely nonverbal, so he can't tell us why he doesn't want to do it anymore. He's not great at expressing his feelings through his AAC device yet, but it's something we're working on. Any ideas on how we can take baby steps to rebuild this trust?