Buy the account and rebrand to similar content. Don't grow the account from scratch, let teenagers in eastern europe and malaysia do that. Try not to get scammed when buying the account.

Anything you do from then on is to offset the decline in followers.

De-risk and break even on doing promos for other people. (lets say you bought a $5k account for $50, do 5-10 promos for other people, done. Start with more capital and get a more compelling account, don't go too big though, 30k is a sweet spot.)

Engagement ratio of 1% is bad, 2% is ok, 3% is great. Not super important when talking with individuals. Only when trying to charge more for a promo, or selling the account.