Warm refrigerator

Good DaY, to whomever is helping me!

My refrigerator will not cool. I thought maybe it was ice build up, so I unloaded all foods, freexe and refrig. Turned off the unit, unplugged it and let it sit for about 14 hours. There was some water in the drain pan below when I looked. After cleaning the inside I plugged the unit back in and turned both refrig. and freezer back on. I thought all was good, as the freezer worke, as it has been and even the refrigerator chilled to the 40 degrees. I was happy! But, 4 days later, same problem. The refrigerator side would not cool. What might it be? If this has something to do with a defrost mechanism, or the behind the scene parts, can I make the repair or do I have to call a repair person. I’m not scared to do it myself, if I understand all I need to do. But, if it’s better to call I will. I just want some idea of what the problem may be so I don’t get ripped off, especially labor. If you could approximate, how long should the job take to make the reapir? Thank you! Dee