I know many of you guys know this answer but I saw people asking this question alot of times. So I will answer the question below:
1) Go to Mobile Deployment sections in the settings page.
2) Now scroll to the bottom, you will find a key icon
3) Just click on it, the zip file will be downloaded
You will find the .jks and the credentials files in that zip folder. You might need pro or teams subscription to do this.