you have to replace with run flat tires if it came with run flat tires. 4/32 minimum tread. Matching set, same rating as the tires that came on it, doesn’t have to be same brand. It’s a common practice to buy used tires for the purpose of lease return that match the criteria.
This is a website that sells used tires: https://www.bestusedtires.com
Also see here: BMW lease return