Specifying multiple file types in SSIS Foreach loop Container e.g: .txt and .dat

I want to Specify multiple file types in SSIS Foreach loop container FILE property under COLLECTION tab. 

Here is the scenario:

Rename the specific files with the specific extension with timestamp (there are other files with the same extension is present as well in the folder). 

 1) customer.txt 

 2) employee.dat

Move these files after renaming it with timestamp archive folder.

I dont know how to give to specific file extension in FILE scetion under COLLECTION tab in for eachloop container.

Thanks in advance!

ZK