The reimbursement of Medicare cost that I paid before SSA approve my benefits, was included in box 5 SSA-1099 SM,where do I deduct the reimbursement?

If the reimbursement was included in box 5 of the SSA-1099 (box 3 minus box 4) then you only need to enter the box 5 amount on your tax return.

Box 4 shows benefits repaid in 2018.  So you do not enter the reimbursement anywhere else on your tax return.

To enter Social Security benefits reported on form SSA-1099

• Click on Federal Taxes (Personal using Home and Business)
• Click on Wages and Income (Personal Income using Home and Business)
• Click on I'll choose what I work on (if shown)
• Scroll down to Retirement Plans and Social Security
• On Social Security (SSA-1099, RRB-1099), click the start or update button

Or enter ssa-1099 in the Search box located in the upper right of the program screen.  Click on Jump to ssa-1099