Do I need a professional or can I repair this myself

you need to clarify what you mean by "CELL" if you are referring to the salt tank you can replace the brine line and it will be fine. After replacing run valve through manual cycle to refill cycle to purge all air from line. Then run through manual regeneration 2x in 24 hrs.
RJ

Sorry about that - the tube runs from the mineral tank to the controller. The controller manual says the tube goes into the "inlet to cell" from mineral tank.

That is the brine line to the "salt" tank. On an Autotrol 155 the brine line goes from the air check assembly (clear housing on right side of valve) to the float assembly in the salt/brine tank. The mineral tank is what the valve is sitting on top of. This is what hold the "media" which softens the water. If that line is leaking, bypass the softener, run it through a manual cycle, take the brine line off and take it to a water treatment dealer for new line. You may be able to use the old fittings.
RM