Our HDB resale seller broke his promise of allowing early renovation, should we sue him? Anyone with experience?

Firstly, our HDB resale application was approved (to be completed in late Nov). Then, seller contra rejected and requested we cancelled and resubmit. So we agreed as long as the seller allowed us to do early renovation and move out based on the 1st application completion date.
(Seller agreed and acknowledged on Whatsapp)

But now seller suddenly rejected our early renovation.

What do you suggest us to do:
1. Move on and get over it. Reno start 1 week later n may not complete b4 CNY and contractor will b closed on Feb thus will only get the unit March.
2. Seek legal advice and sue sellers.