is there any effect on gig ranking when changing gig image?
The only thing that impacts images in any search engine ranking anywhere is the alt text attached to the image. There is no image SEO on Fiverr.
Be more concerned about how well your image engages people.
Thank-you for helping me and clearing my mind
One thing I want to clear? Is it necessary to stop gig when I want to change to a gig?
When you need/want to make changes to your gig, then make the changes to your gig. You cannot control what the search results do, so it would be wise to learn not to be so worried about things you cannot control.
No it isn’t. Not sure where you got that idea from.