Found solution. The following PowerShell code solves the issue.
#Assigning Identity's Username To AppPool
cscript adsutil.vbs SET w3svc/AppPools/YourAppPoolName/WAMUserName Username
#Assigning Identity's Password To AppPool
cscript adsutil.vbs SET w3svc/AppPools/YourAppPoolName/WAMUserPass Password
#Making ApplicationPool Configurable
cscript adsutil.vbs SET w3svc/AppPools/YourAppPoolName/AppPoolIdentityType 3