1998 Jimmy 4.3 Jimmy fuel pump install.

Is the a special tool or technique for getting the locking collar back on? II can get the collar to just barely engage the slotted tabs on the tank opening. All the while I’m pressing down on the new pump with the heel of my hand; the white tab on the pump body is in place and compresses down but just can’t get the collar to fully engage. What’s your thought on this? Thanks, Tim D