Press <Ctrl-\><Ctrl-n>

As this is a pretty awkward keymapping, i’d strongly recommend using mapping it to something else simpler like <Esc> on your config, as shown in the example below:

tnoremap <Esc> <C-\\><C-n>

Otherwise, if you’re using lua, this one might suit better your needs:

vim.api.nvim_set_keymap('t', '<Esc>', [[<C-\\><C-n>]], { noremap = true })

Using [[...]] as string delimiter removes the need to have it’s special characters manually escaped, in contrast to when using quotes, for example: "<C-\\><C-n>"