How can I fix coving that has slightly fell away from wall/ceiling?

My pal and I recently put coving up in the bathroom using cove adhesive.One section has partly come away from the wall and ceiling,the piece is one whole length from a corner and is mitred to the next length on the wall and it is on the join that it is coming away.
It has only detached by a few mm's, it is a little wobbly but not enough to squeeze more adhesive behind.
What is the best way to re-affix this please as taking it down and putting a new length in isn't an option.
Many Thanks,