Replace string and remain the file format

Question

I have a question follow by replace entire string in one column based on matching substring

I would like to replace the string in column 2 with the string in column 3, if the string in column 2 is "unidentified"

I have tried the following code

awk -F'\t' -vOFS='\t' '$2=="unidentified" {$2=$3}1'  

Here is my input

OTU1019 Gibberella  Gibberella_tricincta
OTU1001 unidentified Glomeraceae_sp

It did the task, but it also changes the file format

Here is the output from that code:

OTU1019 Gibberella  Gibberella_tricincta
OTU1001 Glomeraceae_sp
    Glomeraceae_sp

The desired output should be:

OTU1019 Gibberella  Gibberella_tricincta
OTU1001 Glomeraceae_sp Glomeraceae_sp

How do I keep them in a same line after replacing string?

Thanks!