I don't work in Chengdu. How can we transfer social security back to Mianyang? Can Mianyang be changed into a personal one?

Go back to Mianyang first and participate in local social security in Mianyang. If you are registered in Mianyang, you can participate in social security in your own name. If you are registered in other places, you can only participate in social security in the name of the company, which means you need to find a company to help you buy social security.

After participating in Mianyang social security, you can handle the transfer of old-age insurance at Mianyang Social Security Bureau, which will give you an acceptance letter of social security transfer, and you can go to Chengdu Social Security Bureau with the acceptance letter. Chengdu Social Security Bureau can transfer the social security you paid in Chengdu to Mianyang Social Security.