You still didn't show the column InternalName. But whatever, I have made an example that filters by a Text type column. I was going to make an example that filtered by a number type too, but since you just have a text, I'll show that.
I'm going to show my example SharePoint List and List Settings:
Example List View
SharePoint List Settings
To find the column InternalName you need to look in the URL of the edit column.
The column "Request ID Text" has an InternalName of "RequestID_Text"
The column "Request ID Number" has an InternalName of "Request_x0020_ID_Number"
Here is the example form I am using:
Example Form
Example Form Submission
Here is the flow that will trigger when a form is submitted:
Example Flow Overview
Here is the first part of the flow that is filtering the Get Items. Look in the Filter Query to see how it is written and uses the form response as a filter. See how even though my column display title was "Request ID Text" the InternalName was "RequestID_Text" so that is what I use in the filter query.
Flow Part 1 - Get Items Filter Query
If I was using the number column instead of the text the Filter Query would look like this:
Filter Query when using the number column "Request ID Number" with an InternalName of "Request_x0020_ID_Number"
The rest of the flow has the condition that checks the results of the Get Items. It is checking the length() of Get Items values which is basically a count of how many items were returned. If the length is 0 zero, then no items matched the RequestID. So it should make a new item on the list.
Condition is checking the Length() of Values from the Get Items
Flow Part 2 - Condition Check and Update Item
The use of the variable to get the Item ID is to prevent using an Apply to Each. But it also assumes there is only 1 row that will be returned with the RequestID. If there are multiple rows with the same RequestID, this will only update the first one that was retrieved.
The expression has to be manually typed into the field.
first(outputs('Get_items')?['body/value'])?['Id']
Since it is trying to avoid the apply to each the expression is using the body of the Get Items and then references the ID column.
Use the First Item from Get Items ID value
So this is a basic example, but hopefully it gives you an idea of what is supposed to happen.