You can grimp on a new female terminal after you clean up end of wire and crimp it onto wire. Usually depending on wire size you can use one with red/pink color if larger wire use blue color size. Use smallest one you can so it will fit into socket in relay holder.
It won't have a lock tab on it but you usually can force it into socket and hold it there while you reinstall relay.
Rare for me to try and suggest a better approach than Steve's, but here goes. Rather than using coloured crimp terminals, consider obtaining plain brass Utilux or Amphenol (etc.) spade terminals. If not practical to purchase a small quantity (they come in packs of 50 or 100), perhaps purchase a two-, three-, four-, or six-way standard connector pair, which come with identical-sized terminals. In the pic you can see a three-way connector pair that I intend to re-do my brake light switch with, after someone used those horrid (sorry Steve but I really dislike them and they're not up to your usual aircraft-engineering standards

) red crimp-on terminals with no locking capability.
The locking tab is clearly visible in the pic and you'll find that it clicks into the relay holder perfectly.
You can use crimp tool as in my second pic which folds the tabs back on themselves to give the result shown in third pic alongside 'factory' wire (this is a far better crimp than the plastic-insulated terminals ever give, as those are only ever 'squashed'). For best results, twist wire strands and fold back so that you crimp onto a 'double' thickness. Sorry that in my pic you can see that the wire insulation crimp 'missed' slightly due to poor insertion of terminal in crimp tool (I was trying to hold a camera in the other hand but that pic was out of focus anyway). Or you can use pliers and solder (the brass solders easily, though the copper may leach out with the heat).
I just happen to have the crimp tool, and the experience with these, from an extremely monotonous job as an 18-year-old making wiring looms for traffic hazard signs - the types with the high-current sealed beam lamps that display arrows for roadworks etc. We had to find the best way to make them, as we exported them to the USA (Pennsylvania's Trafcon company).
Steve's approach will work of course, but I was just keen to show how I cope with terminals as you mentioned it. Incidentally those relay holders are worth saving from parts cars, as they are difficult to buy new. I use them for any additional relays, to give that 'standard' look.
-Alex