I'm sorry for your loss.
I would start asking questions from those with local knowledge. It would be particularly useful to know what the state of the management of the block is, for instance in relation to repairs, sinking funds, potential future liabilities, etc. You shouldn't make a decision to keep it without that information, so that you can know whether or not your inheritance will turn into a liability.
If you kept the flat would you live in it or rent it out? If you want to rent it out and it is in a bad neighbourhood, could you get good tenants or not? What legal conditions do you need to comply with on renting, and how much work would be needed to the flat to make it legal to rent?
Is the neighbourhood likely to get better or worse? Short term or long term? Is it an area/city which is growing economically and/or in population or an area/city in decline?
You are a newcomer to real estate. Is owning property a part of your life plan? Does owning this property fit into your life plan? Owning property is not for everyone, despite the emphasis some cultures put on it.
If you are going to sell, doing it through a (carefully selected) estate agent is probably the way to go for a newcomer to property and a potentially difficult property to sell. A good estate agent would tell you the value as is and when rehabbed, and you should be able to get a builder to give you an estimate or quote for rehab, which would tell you whether it is worth rehabbing and which would make for the easiest sale. Even if you don't rehab, leaving the property clean and empty is a good idea - house clearance companies will do this for a price if you can't do it yourself.
