Zenfone 4 (A400CG): Replacement display won't sit flush

We have replaced the broken display & digitiser on our Zenfone 4 (A400CG).

The only problem is that the digitiser won’t sit flush into the enclosing bezel because there is insufficient adhesion.

When the previous display was removed there was an adhesive ‘gasket’ which lined the inside edge of the bezel. Unfortunately almost all of it was removed in the process.

As far as we can tell this gasket is not a separate spare part available from anywhere. Maybe it’s a generic item?

Please would someone shed some light on what this material is and where we might get some (we are in the UK).