I am trying to write an IF statement, where if column F = "MOPAR" I want to return column E with "FCA-" to create "FCA-60519" or if column F = "SAFELITE", then I want to return column E with "SGI-05188"
I was trying to use TextJoin, but was just getting errors.
I have tried using TEXTJOIN, but only getting errors.

Assuming the data you're checking is in F2, and the data you're pulling is in E2, no need to overcomplicate. You can even create a table where you say MOPAR in one column and the prefix you want to pull and start with that process in case there's more than 2 cases.
However, if you're only checking for those 2 rules, you can populate the prefix then combine it with whatever is in E2.
=if( F2="MOPAR", "FCA-", IF( F2 = "SAFELITE", "SGI-") ) & E2If it's only the 2 rules, you can further simplify by only checking for one of the examples. However, this will see a non-match for "MOPAR" and always put "SGI-", so you have to be mindful of what other data appears in your dataset
=IF( F2 = "MOPAR", "FCA-", "SGI-") & E2I like to setup a table like below, because as more datapoints are introduced you can add them and easily maintain them without adjusting formulas
and you can name this by using
Ctrl+Tand name it something like_Labelsand do a xlookup or vlookup to pull the prefix then combine it with the value in col e using the&operator.=vlookup( F2, _Labels, 2, 0) & E2