Making two time indices coherent

Question

I am trying to merge two panels of quarterly data df1 and df2. Each panel dimension is country codes and a period range time index.

df1 has time index that begins on the first day of every three months, df2 has quarters ending on 28th (if February), or on a 30th, or 31st.

How can I change this last time index so it begins on the same date?

Thanks