With a new image ready to apply textures to, use Blender's Texture Paint mode to quickly brush texture colors onto your mesh:
- Navigate to Texture Paint mode.
- On the viewport, select the clothing object.
- Open up the sidebar tools to access brush settings.
- Select a color, brush size, and falloff to apply. You might need to adjust settings, depending on the modifications you intend to apply.
- Draw on either the UV 2D map, or the 3D mesh.
- Save the .png of your texture map by selecting Image > Save.