For clause 6.1.1 of ISO 45001:2018 the standard is referring to opportunities at the organizational planning level which can affect your OH&S performance. An example could be finding out that a supplier has made a cleaning chemical that is much safer for your workforce to use that the chemical that you currently employ to clean your product. You could then determine that you will investigate if this chemical will work for you, and if the trials are successful then using this new chemical will reduce the hazards that your have for cleaning your product. Another example could be the identification of a new robot that could perform a particularly hazardous activity in your organization.
The best practice for after identifying the opportunities is to treat them exactly as you would a risk: document and assess the opportunity, determine what, if anything, needs to be done, make a plan to achieve the opportunity and then track his plan to completi on. Then you will be certain that no opportunities to improve your OH&S performance are forgotten.
For a better understanding of the ISO 45001:2018 requirements see our whitepaper: Clause-by-clause explanation of ISO 45001:2018, https://info.advisera.com/45001academy/free-download/clause-by-clause-explanation-of-iso-45001