Patch can be downloaded from Oracle Support site: link
All Upgrades: 730365.1
Patches & Updates → Recommended Patch Adviser → Select the necessary product
Don't forget that you must have also adequate OPatch tool from patch: 6880880
Patching of the Grid Infra is done in rolling fashion, meaning that the patching is done node by node, such way that the database can remain online and available. Of course there is option to patch both: Grid Home and Database home, but again, the database can remain online. There are two main ways to patch Grid Infra home:
(Patching 12.1.0.2)
(Patching 12.2.0.1)