To connect to Excel sheets with exMon you need to install Microsoft Access Database Engine 2016 Redistributable on the exMon machine.
1. Download ACE driver: https://www.microsoft.com/en-us/download/details.aspx?id=54920 and install on the exMon machine. In almost every case you need the 64 bit driver.
2. Create a new Data Provider in exMon, select Excel as the data provider type and for Connection String put:
Provider=Microsoft.ACE.OLEDB.12.0;Data Source=C:\PATH\TO\MY\Book1.xlsx;Extended Properties="Excel 12.0;HDR=YES"
Make sure to have a full path to your Excel sheet and note that you can refer to network paths if the exMon user has enough privileges.
3. Create a Query or Compare Query in exMon and select the newly created data provider.
4. Start by setting the query as
SELECT * FROM [Sheet1$]
where Sheet1 is the name of your sheet in Excel