The Riverwalk
20 Upper Circular Road, #04-01/02
Singapore 058416
There's a map provided at: https://www.mom.gov.sg/contact-us/locations#Tab-EP
Here's the link to Google Maps as well. It's the block between the river and Upper Circular Rd.
The best way to get there is head to Clarke Quay MRT station (train station - coded NE5), where you will come out of a shopping centre called the "Central". Once there you just need to cross the road (Eu Tong Sen St and New Bridge Road - note they have a street name for each direction the traffic is going), and you cross the road by going over an overpass or pedestrian crossing.
Stick to the river if you get lost and look for a building called "The Riverwalk". It may not look like it at first if you're not taking the lift (elevator) and instead taking escalators, but the EP processing centre is at one of the top levels.
If you find yourself near a building that has different colour wooden windows then you're on the wrong side of the river. Make sure you're on the side with Central and you should see The Riverwalk walk nearby too.