how to get first 3 octat of fix version in another custom field

[Fuego Coffee]

Dear Team,

I want to get the first 3 octets of the fix version in another custom field.

Examples:

Fix version is:10.3.2.1

The new custom field should have a value: 10.3.2.0

first 3 octets and then 0 in the last one.

Another example:

Fix version is: 12.4.2.3

New custom field: 12.4.2.0

[David Fischer]

At what point do you want to copy that value? During issue creation? During a transition? Or any time the fix versions field is modified? 

Also, which apps do you have installed for that?

[Fuego Coffee]

the trigger event will be a transition.

The installed app is the script runner