Fiscal Responsibility Laws (FRLs) is best handle by creating a dummy variable that takes the value of 0 before the implementation year and 1 after the implementation year. such that dummy variable can then be interacted with the public debt variable to capture the effect of the FRLs on public debt.

Thank you Chuck A Arize Sir for clearing the doubt.

Check this link.

https://stats.stackexchange.com/questions/345746/testing-for-structural-breaks-by-adding-time-dummies