Question is, do you want the ability to constantly heal like medivac/science vessel or instant heal like queens heal?
For medivac type, you need the "create healer" effect type, for instant heal you need "modify unit".
If you quickly want to test it with a step by step guide, select science vessel (doing it with an instant heal works very similar):
1. Select "nano repair" in abilities
Change target filters - "mechanical" allowed instead required and "can have shields" as required instead allowed
((*Ability target sorts - Change TSlifefraction to TSshieldsfraction)) (I think that is only needed if you need it to cast smart)
2. select "nano repair" in effects
Change "recharge vital" to shields
-> working, but you would need to rename it, change tooltips, the ratio and speed at which it restores shields as you need etc. I tested it.
Question is, do you want the ability to constantly heal like medivac/science vessel or instant heal like queens heal?
For medivac type, you need the "create healer" effect type, for instant heal you need "modify unit".
If you quickly want to test it with a step by step guide, select science vessel (doing it with an instant heal works very similar):
1. Select "nano repair" in abilities
((*Ability target sorts - Change TSlifefraction to TSshieldsfraction)) (I think that is only needed if you need it to cast smart)
2. select "nano repair" in effects
-> working, but you would need to rename it, change tooltips, the ratio and speed at which it restores shields as you need etc. I tested it.