Usually for textile screen printing it is not necessary to sharpen squeegee blades. When it gets to a point where they are too dull, replacing them is the best option. They are very inexpensive and overall the low cost to replace them far outweighs the expense of a squeegee sharpener and the time required to sharpen each blade.
Modern squeegee blades are made from a nylon material as opposed rubber used in times gone by. They stay sharp longer and will resist wear brought on by cleaning agents and solvents. Printers can also invest in triple durometer blades.
Triple duro squeegee blades offer a stiff core with softer outside edges. These blades can last for decades without requiring to be sharpened. Triple durometer squeegee blades usually retail for roughly double the price of standard squeegee blade. It is a bit of a price difference but in the long run may be worth it as they offer other advantages too.
It is important though to ensure that your squeegees are indeed sharp as this one factor alone can have a substantial influence on the overall print quality. Once the squeegee becomes hardened by solvents, develops cracks or other forms of damage, replace them straight away. It is a small price to pay to ensure you maintain high print quality.
So the short answer is – that you do not need to sharpen squeegee blades at all. Just keep an eye on them as they grow older and replace when they become hard and or cracked.