Find and replace part of an item in a SharePoint List

Nic_ol 
No need for a flow, just do the following:

• filter by the value you want to update
• Select all
• Click on edit
• Enter the new value in the edit form in the corresponding cell

Nic_ol 

I thought a Flow might be the easiest way, but honestly, you can just utilize a view and the grid view to update the items. Unless you are talking insane amounts of items. You can create a view, use edit view, and under filter, choose the column then contains and ER. Save and then you get a list of all ER for that column. You can click edit in grid view, then you could if the list fits on the page (100?) you can copy that entire column of data out to excel, do you're replace, then copy the data and paste it over the columns. You could easily create a new column next to the existing one to hold those values as a test to make sure it works as well before trying that change. 

You could do this in chunks with the view as well if there are lots of items or you're other alternitive is utilizing flow, and a combo of get items, a condition with update item action using replace expression.