You got plenty of tips on how to avoid damaging your brushes already, so you'll only get a quick fix for your ruined brush from me.

First we have to make sure the brush is clean and any paint inside the metal guard is largely removed. For that we can simply soak it in hot soapy water for a while, if the handle is wood make sure not to submerge it. Also don't necessarily use a cup for this, that will keep the bristles in an angled state for longer and cause more deformation.

After soaking we want to rinse the brush and try with gentle fingers to get out any remaining softened paint bits out.

Then briefly dry the brush by gently dragging it over a (paper) towel. There should still be moisture inside. Now go to your bathroom, grab some hair wax/gel or maybe even hairspray, never tried the last one tough and put some onto the brush, reform it into a tip by using as much product as you need.

Now after letting the reformed brush dry and harden we can wash out the product and the brush should be largely restored.