autoincrement field not showing in studio formula builder

Hi All,

I have created 2 fields auto increment field (field 1) and textfield(field 2)  and I want calculated formula in field 2 = concate("P",field 1)

but autoincrement field not showing in studio calculated formula builder.

If field 1 = 0001

then field 2 = P0001

Can anyone suggest, without coding how we can achieve above.

Kindest Regards,

Shreya