Please help! I don’t know what to do on what to do about my frozen main water supply line to my toilet?
Oh. I just realised &quot;the line is in the exterior wall&quot; - you mean buried inside a wall itself, or that it comes in from the outside? How close to it can you get? Can you see any part of it to examine it? I've never seen any building with piping buried in exterior walls (just because of this precise winter scenario), so I'm a bit puzzled.
Late Edit
I might have to reduce this to &quot;if you can see the pipe or get to it to see if it's cracked or may leak and you can switch off the water to this one run without affecting the rest of the house, then warm it now. If not, call the plumber.&quot;
What you don't want to end up with is a leak you can't get to &amp; can't switch off without switching everything off, especially if you and a thousand other people are all queuing for the same plumber, who may not be able to make it til Wednesday.

Thawing the pipe is easy enough, a hairdryer or small fan heater &amp; a bit of patience… however…
Ice is 'bigger' than water, so frozen pipes are swollen pipes. Swollen pipes can crack under pressure.
So, before considering your next action - to call a plumber or attempt to DIY - make certain you can see no evidence of swelling or cracking.
If all looks good, then you can gently heat it. If using a hairdryer etc don't get the pipes themselves too warm. Be patient &amp; heat around the area, slow &amp; sure.