Simple refill tube problem

[Lkiia]

Hi all! I know nothing about toilet, just saw this forum and wanted to ask a simple question. Yesterday the refill tube in my toilet tank was detached from the valve. I tried to put it back, but it got stuck like in the picture and I couldn't press it all the way in. I saw that there is a tiny bump that's like a line's shape at the back of the grey part, I guess it is used to secure the tube after it is in, and is now stopping me from pushing it in? I'm not sure.
Anyways, I don't know if I should use all my strength to just press it in, as I'm afraid it is not the right way and I might break something... Any suggestion?

 

[Reach4]

I would say to use more strength, and twist as you push.

 

[Sponsor]

 

[Jeff H Young]

old tubing is stiff use the new tube that came with the fluidmaster or ill heat it up with a lighter or torch BEFORE pushing it on

 

[John Gayewski]

If that came off already then it's probably stretched and will come off again. I would cut the stretched portion out and use a "virgin" end to press back on.

 

[Lkiia]

Thank you for all the replies!!