You can either use the text-to-columns function in Excel, or for better flexibility in separating the first name from the middle names, use the following functions:

Assume you have the first and middle name in the column A.

Then in column B display the first name: =IFERROR((LEFT(A1(FIND(” “,A1)-1))),A1)

In column C display the middle name(s): =IF(ISERROR(RIGHT(A1,(LEN(A1)-FIND(” “,A1)))),””,RIGHT(A1,(LEN(A1)-FIND(” “,A1))))