After you have upgraded Oracle Grid Infrastructure 18c, you can install individual software patches by downloading them from My Oracle Support.

• About Individual (One-Off) Oracle Grid Infrastructure Patches
  Download Oracle ASM one-off patch and apply it to Oracle Grid Infrastructure using the OPatch Utility.
• About Oracle Grid Infrastructure Software Patch Levels
  Review this topic to understand how to apply patches for Oracle ASM and Oracle Clusterware.
• Patching Oracle Grid Infrastructure to a Software Patch Level
  Starting with Oracle Grid Infrastructure 12c Release 1 (12.1), a new cluster state called "Rolling Patch" is available. This mode is similar to the existing "Rolling Upgrade" mode in terms of the Oracle ASM operations allowed in this quiesce state.