Gti injector

Hi can anyone please help me, i want to change the fuel injectors,
I have new injectors new seals new inserts
the problem I have is putting them back together
the seals on the injectors feel so big and I can't fit them in to the inserts
is there any special tool or way of doing this ???
tks
 

Do you have a picture?
Do you have the right injectors as there is 2 types.

Smear a little grease over the rubber seals and that will help them slide home.

Grease definitely helps, and it helps to get the injectors into the right position in the head.