If you import into the EU/EEA 1000 kg or more per year of an individual chemical substance, REACH regulation applies. 31 May 2018 was the last change to submit a REACH registration for existing substances manufactured or imported in amounts more than 1000 kg per year. If the registration obligation applied to you but you did not submit your dossier in time, as from 1 June 2018 you can no longer manufacture or import your substance legally into the EU/EEA.
If you missed the deadline, you should make yourself compliant without delay. With a pre-registration or inquiry number, you can register your substance directly. If you do not have a pre-registration or inquiry number, you need to submit an inquiry to the European Chemicals Agency (ECHA) before registering it. If a registration is submitted to ECHA after 31 May 2018, you will need to wait until you receive your registration number before resuming or starting manufacture or import of your substance.