Recovered need file extension changed?

I recovered my image files but they are listed as file, follow by their number and an extension .CHK.
I need help in opening the images as .jpg. Renaming the extension as .jpg does not work.
is there anyone who has experienced this same problem?
i am seeking a solution and appreciate anyone's help in advance.
My files are on a SanDisk Extreme 16GB micro SD HC 1.
Please, seeking help;
My OS is Windows 10.
thank you.
Joseph