My husband started collecting his benefit at full retirement age and was still worki g and still is. When he retires in a couple years, the three or four years he worked and paid taxes, will it increase his benefit amount or will it stay the same. If it does I crease is it automatic or does he have to contact them and how?
Your husband's earnings since filing for benefits may or may not increase his benefit rate depending on how much he's been earning. Social Security retirement benefit are based on a person's highest 35 years of wage-indexed earnings (https://www.ssa.gov/pubs/EN-05-10070.pdf). Therefore, if your husband earned more in one or more of the last few years than he did in one or more of his previous highest 35 years on which his initial benefit rate was based, then his benefit amount should go up.
Recomputations to include earnings after a person's initial entitlement to benefits are automatic, but your husband could request a manual recomputation by contacting Social Security and submitting proof of his recent earnings (e.g. W-2 forms for wages, or Schedule SE from his tax returns if he's self-employed).