How can I file GSTR- for April-June quarterly after filing GSTR- for April monthly?

If you file your GSTR1 data quarterly, it means you are a quarterly filer. In case of quarterly filing, 
 you need to generate GSTR1 quarterly. During the first and second months, you only have to generate
 the Invoice Furnishing Facility (IFF), which contains only B2B transactions and credit/debit notes issued 
 to registered persons. Here are the steps to generate the IFF:- 
 Step 1: Go to the Display menu.
 Step 2: Click on the GST Report option.
 Step 3: Click on the GST E-return option.
 Step 4: You will see the option for IFF (Invoice Furnishing Facility) E-return. Click on that option.
 Step 5: Define date range, then click on "OK". The three options (Direct upload, JSON, CSV File) will appear,
 and you can use any of these options to upload or generate the IFF of that particular month. 
 On the third month, you have to generate GSTR1 quarterly. Here are the following steps to generate GSTR1:- 
 Step 1: Go to the Display menu.
 Step 2: Click on the GST Report option.
 Step 3: Click on the GSTR1 E-return option. The options for generating GSTR1 will appear (Direct Upload, JSON, 
 Microsoft Excel, Government Template). Use any of these options.
 Step 4: Define the date range of three months (quarterly).
 Step 5: In the same tab, there is an option of "Skip IFF (Invoice Furnishing Facility) invoices". You have to set
 "Skip two months" in front of it. 
 Through this, in GSTR1, all your data of that one quarter, except B2B transactions of the first 
 and second month, and complete data of the third month will remain. So, If you have uploaded one month GSTR1 
 data so you have to clear that one-month data from the GST site first, then upload IFF data for the first 
 two months, and then upload GSTR1 data accordingly.