You can change the bearing...in car...usually by removing the bearings in front of the damaged one. You'll have to pull the bearings you knock through out the valley window. You'll need a helper. You'll need the grab the bearing removed before it's completely loose so that it doesnt fall into the crank/oil pan.
Pretty much...that bearing is toast. Change it.
The reason for the wear should be found and remedied. It looks like it's A. Oil starved ...and B. Overheated. Check main bearing oil feeds alignment to blocks main saddle oil feed.
I am going to go with overheated. I had some cooling issues with the electric fans because I didn’t think a small gap I had. Long story short it got hot but not “too hot” a time or two. This is probably the result of that. Problem has been remedied and doesn’t get above 200 on a hot day towing with ac now.