Sign Sertificate Different with old one

I have publish my apps on google play with other engine (appsgeyser) and then i want to change (replace) with new apk file from MIT inventor
when i update new release in google developer console, they said that my sign sertificate upload is different with old one. It should be the same sertificate upload with old one. I do not understand how to check it and how to change the sign sertificate?
or should i stop publising first in playstore and create the new one release?
please advice


See here: