Help please

I took my class 3 over 10 years ago amd havent used it since the course. Now I'm suddenly at a job driving a 13 speed. I can't remember anything from the course 10 years ago. Starting to get ok at upshifting but I cannot go from 5th to 4th. On this truck you have to push the plunger down to switch from 5th ( high side ) to 4th. Every single time I take it out of 5th then it wont go in 4th no matter what. It wont go into any gear. I end up losing it amd have to stop and start over. I have been using the clutch once per shift, not double clutching.

 

? Clutch, take it out of 5 into neutral, clutch, out it in 4??