Login via administrator, and go to JavaScript console. There, paste following to send all pending emails
frappe.db.get_list('Email Queue', {filters:{'status':'Not Sent'}, limit:100000000}).then(async res => {
for(let i of res){
console.log('Sending', i.name);
await frappe.call('frappe.email.doctype.email_queue.email_queue.send_now', {
name: i.name,
});
}
});