A colleague has put me through and I'll be sharing the solution here.
Firstly, UTM zones typically do not have decimal figures but some very high precision equipments now include decimals in UTM coordinates.
Secondly, the solution is in two stages:
Change the current map's CRS to the UTM zone of your area of study. Right-click on maps in the Contents pane and select properties. Open the Projected Coordinate Systems drop-down and scroll down till you see the UTM subsection. Open the UTM subsection and choose the zone of your study area. Click OK to apply your changes.
In the Absolute X,Y,Z box, click the drop-down for selecting unit of measurement and choose m (for metres). Now you can enter the UTM coordinates including their decimal points.
Note: X is for Eastings and Y is for Northings.