How to "skip" changes in PATCH http request for update a record?

I have a body like this

{
“records”: [
{
“id”: “reccsfBOAsOX5nigv”,
“fields”: {
“test”: 123
}
}
]
}

How can i skip the “test” (currency type) field? The idea is that i have a condition that shall be met. If not, then do not change the “test” field.

Thank you