Now’s a good time to remove any debris in the block by backflushing the engine, allowing it to drain from the open aperture. Clean the aperture using a small wire brush, blade or similar.
Access to the core plug is key to an effective repair. Remove any ancillaries — you might even need to raise or lower the engine
Using a hammer and a suitable drift or chisel, puncture the core plug. If you’re lucky, it might swivel in its aperture. If not, simply prise it out.
Apply sealant if preferred and fit the new core plug, ensuring the dished part goes inside.