My approach as below steps:

1. Remaining expect cycles for next 22 years = 22 x 700 = 15400 cycles
2. f shall be 0.8 base on 15400 cylces
3. Calculate SA = 0.8 x [1.25 x (Sc + Sh) - SL]
4. Check SE = 19582 psi < SA
5. Calculate allowable number of equivalent cycles under 19582 psi stress range
---> N = ( 6 x SA / 0.8 / 19582)^5
6. Calculate allowable year "AY" under 19582 psi stress range
---> AY = N cycles / 700 cycles per year
7. If AY > 22 years, then modification is OK

Any comment?