Hello Prashant,

In a general sense regardless of the application, to perform nonlinear buckling in ansys you may follow the following steps:

1.Create linear static analysis with a small value of your load for the given boundary conditions.

2. then perform eigenvalue Buckling to get the buckling mode for this configuration.

3. after obtaining the buckling mode shape, the nonlinear analysis under the desire loads can be done with one of these options; a) update the geometry based on the first buckling mode to get imperfection or b) impose a small load or displacement to replicate the buckling mode

Eventually, even though it is a different application, this demonstration could help.

https://www.youtube.com/watch?v=YeD_BSpeReE&t=1051s