Input GRM calculated by other software in different format

I am using the GCTA to run the mixed model. I met a problem and could not find any instructions related to my problem on the website. I calculated the genetic relationship matrix through another software myself and wanted to incorporate it into the mixed model when using GCTA. GCTA required a specific format of the GRM.

Now I have a GRM.csv file in a format like this.

I am asking if there is any command that I can use to transfer my GRM to the format required by GCTA.

Thank you so much!

Roxy