The Prophet ﷺ said: “Whoever fasts Ramaḍān then follows it with six days of Shawwāl, it is as if he fasted the whole year.” (Muslim) — for a good deed is multiplied by ten. They need not be consecutive or begin right after ʿĪd.
العربية: عن أبي أيوب الأنصاري رضي الله عنه أنّ رسول الله ﷺ قال: «مَن صام رمضان ثم أتبعه ستًّا من شوال كان كصيام الدهر». (مسلم).
After Ramaḍān, fast any six days during Shawwāl — spread them out however suits you.