It’s not uncommon for mantis to lose their hammers, it happens during a bad molt, but they grow back to full use in 2-3 molt. I have seen it happen with mine, they come back.
i would look into dosing iodine as that will help with encouraging a healthy molt, just keep the dose small, especially while it is in the small tank.
i know you mentioned you were working on the larger tank, which is a good idea, a peacock of that size is likely not happy in that sized tank and a stressful molt is tough for a mantis to survive and it def won’t help with hammer growth.
hopefully yours doesn’t become a Lazy bum like mine did once it lost its club! now he just chills and knows he’ll get his shrimp, used to destory clam shells with one punch.
good luck!