When it comprises 100% of the lawn, tall fescue (TF) makes an acceptable lawn. In KY bluegrass (KBG), textural differences and "clumpiness" make it a weed.

There was at one time a couple of herbicides labeled for selective removal of TF from KBG. These are no longer labeled for residential use.   So, you have fewer control options.    

Here are your options to remove it, none of them quick or easy.

1. Spray now each clump of TF with original Roundup or another trade name herbicide that contains glyphosate as the only active ingredient. Follow herbicide label directions.  Remove dead grass after 2-3 weeks and re-seed with a perennial rye-KBG blend.

2. If there are many contiguous TF clumps in an area, you could mark out the area with string and nails pushed in the ground. Make the stringed area as rectangular or square as possible. Spray original Roundup (or another trade name herbicide containing glyphosate as the only active ingredient) inside the string boundary. This will kill TF - and some of the desired rye-KBG too.  Replace dead grass with new KBG sod.

3. TF greens up earlier in spring than does KBG, probably mid-late March.  You can spray the tall fescue then with glyphosate (original Roundup™ or other trade names).  There will be little or no harm done to the still-brown KBG.   Remove dead TF clump and re-seed the bare spot.

4.   Since tall fescue tends to grow faster than KBG, it often “sticks up” above the KBG. You can paint glyphosate (original Roundup™ or other trade names) onto some of the green tall fescue blades using an artist’s paintbrush.  Or, swipe tall fescue carefully with a glyphosate-soaked rope (Rope-wick herbicide applicator, photo below).  Re-seed bare spots after removing dead TF clumps.

ye-KBG too. Replace dead area with new KBG sod.