What platform are you using as on Android you can navigate to the folder containing your worlds and make a copy of them in a separate folder. Open my files navigate to internal if you have it installed on device storage or SD if you installed to external memory. Then find games in there open com.mojang and copy the minecraftworlds folder to another location such as documents. Once done reinstall and copy not cut and paste the folder back in com.mojang. if on pc look on your installation drive and find appdata folder under the users file and your pc login profile name and you will find them in the mojang/Minecraft folder do same as for Android and simply copy the saves folder to a different location. You may need to click on view and select show hidden files and folders to see the appdata folder but they are there in the roaming folder of your appdata. For Mac and iOS I can't help you.
John Pyzer
What platform are you using as on Android you can navigate to the folder containing your worlds and make a copy of them in a separate folder. Open my files navigate to internal if you have it installed on device storage or SD if you installed to external memory. Then find games in there open com.mojang and copy the minecraftworlds folder to another location such as documents. Once done reinstall and copy not cut and paste the folder back in com.mojang. if on pc look on your installation drive and find appdata folder under the users file and your pc login profile name and you will find them in the mojang/Minecraft folder do same as for Android and simply copy the saves folder to a different location. You may need to click on view and select show hidden files and folders to see the appdata folder but they are there in the roaming folder of your appdata. For Mac and iOS I can't help you.