To convert GMAT scores to GRE scores, there are specific methods and formulas. These two tests cover different topics and use different scoring systems, so you can't convert them directly or we can make estimate but not the official score conversion. However, using this formula, you can estimate your GRE score from your GMAT score.
As far as i know, you can use this formula to convert GRE verbal and quantitative scores to a GMAT total score:
GMAT Total Score=6.38×GRE Verbal Reasoning Score+10.62×GRE Quantitative Reasoning Score−2080.75
Take your your GRE verbal and quantitative scores, within range from 130 to 170 approx.
Use the below table to convert your GMAT scores based on different GRE scores ranges:-