I used these snippets:

In cmp.lua:

return {
  "hrsh7th/nvim-cmp",
  opts = function(_, opts)
    local cmp = require("cmp")
    opts.mapping["<Tab>"] = nil
  end
}

In astrocore.lua:

return {
  "AstroNvim/astrocore",
  options = {...},
  mappings = {
    i = {
      ["<CR>"] = "copilot#Accept('\\<CR>')"
    }
  }
}