Air bleed magnetic filter plumbing advice

Air bleed magnetic filter Can someone please advise how to bleed air from a magnetic filter installed on a Worcester Greenstar boiler. I don’t want to clean it out as that was done by a professional engineer who seemingly left me with this problem. Specifically, should I close the valves either side of the filter before opening the top bleed valve? Should the boiler be turned off? Etc, etc
Comments appreciated.

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