gstr1 quarterly or monthly option can be changed
If you have by mistake selected GSTR1 return filing option as quarterly instead of monthly or monthly isntead of quarterly, you cannot change it.
The option of monthly or quarterly return filing is for a financial year and cannot be changed in one single financial year.
While selecting your return filing period be careful as this option is available only once in a financial year.
Even if you have by mistake selected wrong tenure (monthly or quarterly) you can change it in next financial year.