Bottom drawer Malm 6 drawer

Hi all

I bought the Malm 6 drawer chest approx 2 months ago but have just built it.

The top 5 drawers are fine but the bottom drawer cant hold anything as it slips off its runners everytime its openend & closed. Occasionally it wont close at all & has to be completely taken out & replaced.

Anyone know how to fix this? I would like to avoid having to take it back as it would have to be taken apart to be returned & then ill have to spend 3 hours building the new one!

thanks