First you need to download Lambda's map editor:
https://www.mod-rdr.com/downloads/rdr2/mods/67-red-dead-redemption-2-map-editor/

*Important* - Currently this map only works with version 0.1.6.1 and lower. Future versions may require a map conversion tool.

Put the 'Limpany_Restored.xml' map into 'Rockstar Games\Red Dead Redemption 2\MapEditor\Maps' folder.

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|*UPDATE*|
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Since Lambda is not currently actively working on the RDR2 Map Editor anymore I have now converted all my maps to native ymap format which can be loaded in using Lenny's Mod Loader.
Download lml(Lenny's Mod Loader) Here:
https://www.rdr2mods.com/downloads/rdr2/tools/76-lennys-mod-loader-rdr/

Put 'Limpany_Restored.ymap' into 'Rockstar Games\Red Dead Redemption 2\lml\stream folder. If streams flder doesnt exist, simply create one and place it in.
The map will now be loaded permanently in-game when you load in.

*Note - Unfortunately not everything converted properly with the ymap, like the deleted props and NPC's. The xml version in this mod is the better version.