For everyone struggling with the SMD electrolytic capacitors (I know I was!). Here’s a method I found working for me (using a soldering iron).
I’m using a 1.6mm chisel tip at 300deg C and soldering paste (plus a tiny bit of leaded solder). You’ll also need some tweezers.
Put some solder paste onto the pads (we’re soldering C18 here).
Place the cap carefully onto the pads (mind the orientation!). This step is crucial. Try to align in properly so that it is horizontally and vertically centred using the same amount of space on the pads.
Clean your tip thoroughly (!) and put a tiny bit of leaded solder onto one side to transfer the heat a bit better. Use the tweezers to hold the cap in place. Gently press it down a bit from the top. Carefully touch one pin/pad with the soldering iron - don’t use too much pressure - and wait for the solder paste to flow (roughly 2-3 seconds). Remove the iron. Hopefully leaving a beautifully soldered pin.
Clean up the excess solder paste (I used flux remover but any PCB cleaner will do I guess).
Fingers crossed, I hope it’ll work for you! Let me know in the comments if I forgot anything or whether this can be improved somehow.
P.S. Here’s the video in which I first saw this method being used: there’s also two other methods, one of which might work better for you.