how can I export contacts from Android to iPhone?

That would depend on what type of format your Android software allows you to export your contacts in. What does your manual say about how to export contacts and what format they are exported in? Does it export them as a vCard? a CSV file? something else?

Try emailing the vCard to yourself, then open it on your iPhone and tap the vCard attachment to import them. This will only work if you have a compatible vCard. If it doesn't, create a Gmail account and try to import the vCard to Gmail (see https://support.google.com/mail/answer/183711?hl=en). Then export the contacts from Gmail as a vCard (see https://support.google.com/mail/answer/24911?hl=en). Email the vCard from Gmail to yourself, open the email on your iPhone and tap the vCard attachment to import the contacts.

You're welcome.