Freezer is working fine, but frig is warm,

If you found ice in the freezer then there is usually a lot more behind the back plate. If you let it defrost completely it should work good for a couple days until the ice builds up again. you more than likely have a deefrost issue. There are usually nthree components in a typical defrost circiut. The heater, defrost thermostat and a defrost timer or control. one or those is bad.

First try melting the ice with hair dryer. See drain tube going to pan under frig? It can get clogged/frozen with ice. I cleaned mine with very warm water shot out of a water pik. Or u can hair dryer it, then pour warm water on the little pan that holds the drain tube. Be sure that tube is clear for draining.Otherwise, more ice at vents.

That ice is the reason that the freezer is working but the refrigerator is not cooling. That ice is
blocking the vent that allows cool air to leave the freezer section andfall down into the refrigerator
section.
The fix is free: defrost the frig - pull the plug, and let that icce melt out of there, clean up the
wet mess, and turn the frig back on - problem solved.
Keep the vent area free of ice (and other blockages, like frozen peas covering over the vent), and
you'll keep the problem from recurring.

Sounds like a defrost failure.
Look on the back wall of the freezer from the inside.
If it is covered in ice your defrost system has failed.
Also check the fan motor in the freezer.
If it is not running it must be replaced.

therther is ice built up on the vent in the back of freezer use a hair dryer and melt the ice in the vent and it should be fine

Good day,
This problem appears in spades this time of year, every year.
The problem becomes more severe when the temperatures in the house cools down and is made even worse if the usage of the machine becomes lighter.

It occurs when the machine is off, not on.
There is an open vent, near the bottom, between the freezer compartment and the fresh food compartment. This opening or vent is necessary when the machine is running, so that the air pumped into the top of the fresh food section, can return to the freezer compartment. This is by design.
Now,
When the machine is off, the zero degree air from the freezer compartment. can drift into the fresh food compartmnet and drop the temps near the bottom to below freezing.
Off time increases substantialy at this time of year.
Some have even recommended turning the controls colder to offset the problem, but I've no proof it works well, or even a little.
SXS and top freezer models experience it more than bottom freezer models.

You may think the freezer is fine, but stick a thermometer in to be sure. It should be around 0 degrees F. If not, you may have iced up coils. See some other posts on this site about getting to those coils and defrosting.

There is something in the path of the vent. Either some ice or debris.

If you are sure the fan is running either the damper motor (vent in fridge section) is bad and not opening or there is ice in the return vents and not letting air circulate. Take out the bottom drawers in the fridge and look down the two return vents in each corner with a flashlight. If they are iced up the top will not cool.

you could find ice behind the back panel - worth a check. however the problem is probably ice in the return vent from fridge to freezer and the only way to cure is to switch off and leave for a day with doors open. if im right and you try this, if it re-occurs you may have a problem with the defrost system