Hi @Anonymous,
Could you please share a bit more about your scenario?
Further, could you please share more details about your SharePoint list?
I agree with @ScottShearer's thought almost, I think the if() function could achieve your needs. I have made a test on my side and please take a try with the following workaround:
The Column B field set to following formula:
if(equals(triggerBody()?['Column_x0020_A'],'1234'),'Test',triggerBody()?['Column_x0020_A'])
Note: The Column A and Column B are both Single line of text type column in my SharePoint list. In order to include the Dynamic content within your if expression, you should firstly select the if expression, then select the Dynamic content tab and simply click the field you want to use.
The flow works successfully as below:
If the Column A is equal to 1234:
If the Column A value is not equal to 1234:
More details about using expression in flow actions, please check the following article:
Use expression in flow actions
More details about the if() function, please check the following article:
https://docs.microsoft.com/en-us/azure/logic-apps/logic-apps-workflow-definition-language#logical-functions
Best regards,
Kris