This is now the third time you are asking this question. Please do not create new threads to re-ask your question. There was plenty of advice in your previous thread. https://communities.sas.com/t5/Statistical-Procedures/nonlinear-piecewise-regression/m-p/635142
This may give you some clue.https://documentation.sas.com/?docsetId=etsug&docsetVersion=14.3&docsetTarget=etsug_arima_examples06...
And this :
https://documentation.sas.com/?docsetId=etsug&docsetVersion=14.3&docsetTarget=etsug_arima_examples04...
@Ksharp thank you
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