Your covers are not ruined.
With liquid lanolin, you're right, you do not need to heat it. Put lukewarm water in the sink or a big bowl, enough to cover all of your covers. Add enough liquid lanolin to turn the water milky white. Add your covers, (I usually do one at a time) and squeeze them in the water to get the lanolin worked in. Squeeze out the excess water and hang or lay flat to dry. A 4oz bottle of liquid lanolin will last about 4-6 months for me, and I have somewhere around 16-20 wool covers that I use.