Hmmm. I wouldn''t really recommend that video. A new soldering iron bit should tin easily, AS LONG AS YOU APPLY SOLDER IMMEDIATELY, but you have to rub the end of the solder into the bit surface so the flux cores melt with the solder, and keep the temperature down to just above the solder melting point. so for non-temperature contrplled irons, as soon as the solder starts to take, switch off, and carry on applying solder till it becomes more difficult to melt then switch back on, continuing till all the active tip surface has been tinned. Wrapping the solder round the bit like that video DOES NOT WORK WELL - there is no flux on the outside of the solder so as it first melts it oxidises and then its no longer being pressed against the bit and most of it just drops off without taking. If you want to try wrapping the bit in solder, you'd need to add extra flux then wrap it in a little aluminum foil to hold the solder against the bit even after it's melted.
Acid flux is evil stuff - Apart from the toxic fumes, it usually has acid Zinc Chloride as the active ingredient, which (+ added moisture) is corrosive to iron and steel parts of the iron, so if you use it for tip tinning, after tinning, you should ideally remove the tip and wash it thoroughly in boiling water to remove any residual acid. Ammonium Chloride flux is a little less evil, but its residue should still be cleaned off properly.
Tip tinner/cleaner - a compressed cake of Ammonium Chloride mixed with finely divided solder particles is much easier to use for tinning. Simply scrub the ckeaned bit surface across the face of the cake - don't dig it in as that just breaks up the cake, and causes the solder powder to form big blobs of solder that are less effective. You will probably still need extra solder, but the tip tinner/cleaner does most of the work for you.
Also, if a plated bit is FUBARed, its often salvageable as a plain copper bit by grinding back the plating and reshaping it as needed. Plain copper bits don't last well, especially at higher temperatures, (as, with every joint, some copper from the tip dissolves in the solder unless it already contains around 2-3% copper) but you should be able to get enough extra life out of it to tide you over while you order and wait for the spare bit you should have had in stock. Bits are wear items - order a new one as soon as you put your spare into service.
Using sheet abrasives like sandpaper really doesn't work that well - there's a tendency for the edges of the bit to get more abraded, breaking through the iron plating, and ruining the bit. Also they don't stand up to a hot bit so its difficult to spot clean an area that wont tin. A fine grained oilstone can be used *extremely* gently, but I recommended a fiberglass abrasive brush, because its harder to damage the plating with one. Steel wool can be used on badly oxidised bits if you have nothing better, but as it may be harder than the iron plating shouldn't be used for regular bit cleaning as you are working. You also shouldn't need it for tinning a new bit - if you do it means you screwed up and let it oxidise before you applied flux and solder.