A refundable credit means you can get it back on your tax return. It is included in your total refund. Turbo Tax will automatically add it to your refund.
For 2021....the max for Social Security is $8,853.60 on $142,800 of wages (142,800 x 6.2%). I don't know the max for 2022 yet.
You get excess SS back if one person had more than 1 employer and those employers took out more than the max of $8,853.60 (for 2021). If one employer took out more than the max you have to get it back from the employer.
Check 1040 Schedule 3 line 11 which goes to 1040 line 31.
A credit being refundable means that you get a refund for the full amount of the credit, even if it results in getting a refund that is more than the total amount of federal income tax that was withheld. In other words, in some cases you could get a "refund" of more than you paid in.