If you can wait get an ebay blank no holes in middle just 2 holes to fit on(stainless steel £3.50), if you cant wait cut a coke can apart or similar thin metal sheet , i just wouldnt leav anything like that in for too long with heat and pressure waves it may fail after some time but will last ok to test.
Search and probably plenty of posts with pics maybe on egr blanking.
Ideally what your lookung for is that the maf value changes when you fit the blank.
If with egr working( you had 250 act with 270 desired) this should go up to 485mg/i or somewher near.
If its not say less than 450 you still have air bypassing maf from somewhere or bad maf, try to log on road again and log maf ,desired boost ,actual boost and revs .
Dont forget the map sensor , your already leaning over inlet manifold , 1 plug to remove,1 bolt to remove(hex or tx) then gently twist and pull out if tight dont yank they are only plastic.
Spray off carb cleaner or contact spray will clear out oily sooty crud dont poke anything in it theres a temp capsule at the end,same again search and you will probably find a guide with pics.
Heres a vid( not me) id go a bit gentler on pulling it out than this guy.
Heres one for egr blank( you could probably cut can the width of the bolts in a rectangle and slip inbetween bolts rather than cut to shape( if temporary))
Not your car but egr looks similar.