Formula to insert future date in cell, if specific information placed in other cell

Hello,
I have to track information with a resolution date, however as I am not the only one using the spreadsheet, I want to eliminate the risk of someone "forgetting" to put a date in a field.

Basically, if you review the attachment, in columns C or E, if option LR or HR is put in the cell, I need a resolution date in columns D or F (as applicable).

I assume it would be the IF formula that I would use, but can you advise how to set it up so when LR/HR is input in the cell, the resolution date is automatically set for one month later?
e.g. When LR (or HR) is entered in Cell C2, cell D2 would automatically show a date one month from then.

I hope that this makes sense...
Thanks

Jen

This is brilliant, thank you :-)

Jen