Well in the past I have scraped the top 2" of compost off sprinkled a handful of slow release granules and replaced the top compost with fresh.
you could use a foliar feed like miracle grow that you just spray onto the leaves when needed.

welcome to GoY too. :o)

Hi, welcome to GoY, if it's been in the same pot for a long time, it's quite probable that the plant has filled the available space with roots, and is now potbound, this will prevent the plant from taking up any nutrients that MAY be left in the compost, and if this is the case, no amount of fertilizer is going to make much difference, it will need repotting into an even larger pot, and the roots which are likely to be going round in circles inside the pot need to be teased apart, to get them free of the continual circling of the pot, and use a good quality, soil based compost, Derek.